In modern motor vehicles, soft chassis springs are used for a high driving comfort. In combination with correspondingly designed shock absorbers, such an improved ground contact is guaranteed in case of road unevennesses. The unfavorable increase in the rolling angle in curves which occurs in this case is compensated by the use of stabilizers, whereby the stabilizers are attached to the vehicle chassis and are connected in an articulated manner at the ends to a spring-mounted wheel carrier part, e.g., a suspension arm or a rigid axle via a rocker pendulum each. However, the possible axle twisting is reduced by the use of stabilizers, since they restrict an inward deflection in the opposite direction of the wheels of an axle. Therefore, it is especially desirable for off-road vehicles, so-called SUVs, to make it possible to influence the stabilizer function during off-road driving. This can be guaranteed by the use of switchable components, such that the wheels of an axle can deflect from one another independently. In this way, all wheels of the vehicle hold contact with the ground and can transmit propulsive forces.
There is a possibility of using switchable components in the use of hydraulically length-variable adjusting elements, such as, e.g., piston-cylinder units, instead of fixed rocker pendulums, as this is disclosed, e.g., in U.S. Pat. No. 5,217,245. The length-variable piston-cylinder units arranged between the stabilizer and the motor vehicle chassis show a piston with through piston rod held movably in the cylinder, whereby the piston splits the cylinder into a first and a second cylinder chamber. The first and second cylinder chambers are connected to one another via an external bypass line, which can be blocked and unblocked by means of a valve, arranged outside of the cylinder, whereby two other, internal bypass lines are arranged in this line, each of which connects one end area of the cylinder to a middle area of the cylinder. In the middle area, the connections of the two other internal bypass lines are spaced apart from one another, and a nonreturn valve each is arranged in these internal bypass lines in such a way that only a flow of hydraulic fluid from the middle area of the cylinder into the end area of the cylinder is made possible. In case of an open connection of the external bypass line, the piston can move freely in the cylinder, such that the stabilizer action is neutralized. If the piston is located outside of the middle position and if the external bypass line is closed, the piston can only move in the direction of the middle position, since hydraulic fluid cannot reach the middle area or the other end area from the end areas via the nonreturn valves. As soon as the piston reaches its middle position, it is fixed in same, since an exchange of fluid between the cylinder chambers is no longer possible.
The drawback of this embodiment is especially that the middle position, in which the piston is fixed and thus a stabilizer action is created, cannot be defined precisely. Considerable tolerances are given here because of the connecting dimensions and the connecting holes.
Another embodiment of a switchable rocker pendulum for a stabilizer arrangement of a motor vehicle is disclosed in U.S. Pat. No. 4,973,077, whereby here as well a bypass line, which can be blocked and unblocked by means of a valve outside of the cylinder, connects two cylinder chambers, which are separated by a piston, to one another in their end areas. Two compression springs, which rest against the respective cylinder bottom, are arranged on both sides of the piston within the cylinder. In this case, a connecting hole, in which two nonreturn valves with opposite action are arranged, is arranged in the piston. If the piston is located outside of its middle position, these nonreturn valves make possible an exchange of fluid between the two cylinder chambers with the bypass line blocked, such that the piston can move into its middle position by means of the spring force of the compression springs. In the middle position, the piston is held there since the nonreturn valves in the piston are closed and thus an exchange of fluid may no longer take place. The stabilizer action is present in this position.
The drawback of this arrangement is again that the middle position of the piston for the stabilizer position cannot be accurately defined. In addition to tolerances present in the system—in particular, the springs may have different values - there is the wear of the springs, which leads to additional deviations from the middle position. Moreover, this arrangement has a very expensive design consisting of many individual parts.